California sea lions bark into hydrophones

Early this morning, a couple hours before sunrise, the repeated barks of a California sea lion were recorded automatically on the Orcasound hydrophones. This is the first time I can recall California sea lions being recorded in Haro Strait. The automated detections (tabulated below) were recorded from 04:47:49-04:55:33 PST.

Jeanne Hyde was awoken by the sounds and recorded most of the event which included some loud (close?) barks and a few lower-frequency sounds — perhaps the barks of a more distant sea lion. Her continuous recording (04:49-04:57 PST) reveals that the sea lion made many calls in bursts of 1-3 (mostly 2) barks, for periods of 15-30 seconds, typically followed by a 5-10 second break that often included a low-frequency sound (like groans). Within each burst barks were separated by 0.4-0.5 seconds, while bursts were separated in a sequence by 0.5-0.7 seconds. After about 4 minutes of this barking pattern, there was a 100 second quiet period, followed by another 2.5 minutes of barking during which the intensity slowly fades.

During the burst sequences the mean calling rate was ~1.2 barks/second — a rate that is midway between the underwater bark rates of a calm (1.0 barks/second) and aggressive (1.4 barks/second) adult male California sea lion (Schusterman, 1977). This suggests the barking sea lion in Haro Strait was in a moderately energetic behavioral state. This barking rate is also the best evidence we have that the barking was happening underwater; Schusterman (1977) noted that the in-air barking rate for a given behavioral state was 2x the underwater rate, and ventured that this — combined with the rarity of bubbles being emitted — suggested the sea lions recycle their air during underwater barking!

The barks have strong harmonic structure with the fundamental ranging from 500-700 Hz. The groans are not harmonic and have most of their power between 300 and 800 Hz. Other recordings of California sea lions randomly found on the web seem to have bark fundamental frequency ranges that are a little lower (200-500 Hz for barks and 200-600 for groan from naturesongs.com). Perhaps this suggest that the sea lion this morning was not an adult, or was a female instead of a male?

There were no transient vocalizations or clicks auto-detected before or after the sea lion sounds, either at Orcasound or Lime Kiln (5 km to the south). It is fascinating to learn from Schusterman et al. (1972) that the audiogram of Zalophus californianus (shown below) is pretty flat and most sensitive from 500 Hz to 30 kHz, but then becomes much less sensitive very quickly near 35 kHz. This extension of their hearing sensitivity way beyond their bark and groan frequencies suggests there is strong natural selection for the ability to hear at the peak power frequencies of killer whale echolocation clicks (20-50 kHz).

California sea lion audiogram (Schusterman et al., 1972)

I didn’t find a lot from a quick web search for underwater sea lion barking, but there is this fun video with audio that sounds similar to our recordings: http://jackiehildering.smugmug.com/Animals/Steller-sea-lions/11380690_d8BPVm#!i=800065493&k=VbmZE Notice how the CA sea lion barks get a bit less intense when the animal in frame turns its head away from the camera. Filmed by Jackie Hildering off of Northern Vancouver Island, these sea lions are highly habituated to humans due to interactions at the local fish processing plant.